Various polymers, such as for example polyethylene and polypropylene, as well as various diene-based synthetic elastomers and polystyrene containing such elastomers have sometimes been stabilized against degradation caused by exposure to atmospheric ozone by containing a tris(nonyl phenyl) phosphite (referred to herein as “TNPP”).
In practice, the TNPP apparently functions as a stabilizer for carbon-to-carbon bond containing synthetic rubber as, for example, by inhibiting crosslinking of the synthetic rubber caused by exposure to, and thereby reaction with, atmospheric ozone, particularly free radicals formed by the ozone which may include, for example, various peroxides. By such reaction, products such as for example, a phosphate and corresponding alcohol may be formed by reaction with the TNPP.
In practice, however, the TNPP can hydrolyze in the presence of water to form, for example, di-substituted phosphates such as, for example, a dialkyl or diaryl hydrogen phosphate, which is less active as an antioxidant for the synthetic elastomers than the TNPP. For example, see U.S. Pat. No. 5,532,401. Such TNPP degradation by hydrolysis may be evidenced by the presence of nonyl phenol formed by such hydrolysis based degradation.
For this invention it is desired to evaluate providing a resistance of such hydrolytic degradation of the TNPP and thereby a more effective stabilization of diene-based elastomers such as polybutadiene and polyisoprene and products containing such elastomers stabilized by providing a combination of the TNPP and tetramethylethylene diamine (TMEDA).
For the preparation of the elastomers, at least one of 1,3-butadiene and styrene monomer(s) is polymerized with the aid of initiator/catalyst in a organic solvent solution to form a polymerizate (sometimes referred to as a cement) comprised of the solvent and, for example, the polybutadiene or polyisoprene elastomer. Such elastomer may be recovered from its polymerizate by steam stripping the solvent from the polymerizate which necessarily subjects the elastomer to an exposure to water at an elevated temperature from the steam condensation.
For this invention, it is desired to use TNPP as an antioxidant to retard or inhibit degradation of such recovered elastomer upon exposure to atmospheric ozone by providing the TNPP as an ingredient in the polymerizate from which the elastomer containing the TNPP is recovered from the polymerizate by stream stripping the solvent away from the polymerizate to yield the recovered elastomer containing the TNPP.
Such recovery of the elastomer from its solvent by steam stripping will necessarily require exposure of the TNPP to water formed by steam condensation in the steam stripping process. Such water exposure, particularly at the elevated temperature of the condensing steam, promotes hydrolysis of the TNPP to thereby render it less effective as an antioxidant for the recovered elastomer.
Therefore, it is desirable for the TNPP to have a resistance to such hydrolysis and therefore to have hydrolytic stability upon exposure to water from the elevated temperature stream stripping process used for recovery of the elastomer from its polymerizate.
For this invention, it is desired to evaluate providing a resistance to hydrolysis of the TNPP in the presence of moisture, particularly at the elevated temperature of the steam stripping process.
For such evaluation, it is desired to evaluate providing a resistance to hydrolytic degradation of TNPP with tetramethylethylenediamine (TMEDA). The inclusion of the TMEDA may be viewed as promoting hydrolytic stability for the TNPP antioxidant particularly upon the TNPP being exposed to moisture at an elevated temperature as well as promoting hydrolytic stability for the TNPP in general to therefore enhance an effectiveness of the TNPP as an antioxidant for diene-based elastomers such as polyisoprene and polybutadiene.
In the description of this invention, terms such as “compounded rubber”, “rubber compound” and “compound”, if used herein, refer to rubber compositions containing of at least one elastomer blended with various ingredients, including curatives such as sulfur and cure accelerators. The terms “elastomer” and “rubber” may be used herein interchangeably unless otherwise indicated. It is believed that such terms are well known to those having skill in such art.